METHOD AND APPARATUS FOR TRANSMITTING PPDU ON BASIS OF S-TDMA IN WIRELESS LAN SYSTEM

The present disclosure relates to a scheme for performing S-TDMA in a wireless LAN system and, most particularly, to a method and device for transmitting a PPDU by using/based on an S-TDMA scheme in a wireless LAN system.

Discussion for a next-generation wireless local area network (WLAN) is in progress. In the next-generation WLAN, an object is to 1) improve an institute of electronic and electronics engineers (IEEE) 802.11 physical (PHY) layer and a medium access control (MAC) layer in bands of 2.4 GHz and 5 GHz, 2) increase spectrum efficiency and area throughput, 3) improve performance in actual indoor and outdoor environments such as an environment in which an interference source exists, a dense heterogeneous network environment, and an environment in which a high user load exists, and the like.

An environment which is primarily considered in the next-generation WLAN is a dense environment in which access points (APs) and stations (STAs) are a lot and under the dense environment, improvement of the spectrum efficiency and the area throughput is discussed. Further, in the next-generation WLAN, in addition to the indoor environment, in the outdoor environment which is not considerably considered in the existing WLAN, substantial performance improvement is concerned.

In detail, scenarios such as wireless office, smart home, stadium, Hotspot, and building/apartment are largely concerned in the next-generation WLAN and discussion about improvement of system performance in a dense environment in which the APs and the STAs are a lot is performed based on the corresponding scenarios.

In the next-generation WLAN, improvement of system performance in an overlapping basic service set (OBSS) environment and improvement of outdoor environment performance, and cellular offloading are anticipated to be actively discussed rather than improvement of single link performance in one basic service set (BSS). Directionality of the next-generation means that the next-generation WLAN gradually has a technical scope similar to mobile communication. When a situation is considered, in which the mobile communication and the WLAN technology have been discussed in a small cell and a direct-to-direct (D2D) communication area in recent years, technical and business convergence of the next-generation WLAN and the mobile communication is predicted to be further active.

This specification proposes a method and device for transmitting a PPDU by using/based on an S-TDMA scheme in a wireless LAN system.

An example of this specification proposes a method for transmitting/receiving a PPDU based on S-TDMA.

This embodiment may be performed in a network environment supporting a next generation wireless LAN system. The next generation wireless LAN system is an improved wireless LAN system version of the 802.11ax system being capable of satisfying backward compatibility with the 802.11ax system.

Firstly, the terms will be defined. A trigger frame, HE TB PPDU, HE-SIG-A field, HE-STF field, and HE-LTF field may all be PPDU and fields that are defined in the 802.11ax system. S-TDMA TB PPDU, S-TDMA SIG-A field (first signal field), S-TDMA STF, and S-TDMA LTF may be PPDU and fields that are defined for performing S-TDMA in a next generation wireless LAN system. The trigger frame may be a trigger frame that is newly defined for performing S-TDMA in a next generation wireless LAN system. However, the PPDU and fields that are defined for performing S-TDMA may be generated by using/based on each subfield of the HE PPDU without any modification in order to satisfy backward compatibility with the 802.11ax system.

This embodiment may be performed in a transmitting device, and the transmitting device may correspond to an AP. A receiving device may correspond to a (non-AP STA) STA having S-TDMA capability.

An access point (AP) transmits a trigger frame to a first station (STA) and a second STA.

Based on the trigger frame, the AP receives a first trigger-based frame from the first STA and receives a second trigger-based frame from the second STA. The first trigger-based frame and the second trigger-based frame may be S-TDMA TB PPDUs and may be newly defined in a next generation wireless LAN system. Additionally, the first trigger-based frame and the second trigger-based frame may be generated by using/based on a High Efficiency Trigger Based PPDU (HE TB PPDU). That is, the first trigger-based frame and the second trigger-based frame may be S-TDMA TB PPDUs being generated by reusing the HE TB PPDU.

The trigger-based frame includes a common information field and a user information field.

The common information field includes S-TDMA indication information on that the S-TDMA may be performed. The S-TDMA indication information may include a reserved bit within the trigger frame or may include a reserved bit within a trigger type subfield being included in the trigger frame.

The user information field includes allocation information for a first RU to which the first trigger-based frame and the second trigger-based frame are to be transmitted, a first symbol offset information for the first trigger-based frame, and a second symbol offset information for the second trigger-based frame. The first symbol offset information and the second symbol offset information may be included in a Trigger Dependent User Info field, which is included in the user field.

The first trigger-based frame is transmitted in the first RU during a first symbol, which is determined by the first symbol offset information. And, the second trigger-based frame is transmitted in the first RU during a second symbol, which is determined by the second symbol offset information.

The first symbol offset information may include information on a transmission start point (Starting Symbol offset) of the first trigger-based frame. The second symbol offset information may include information on a transmission start point (Starting Symbol offset) of the second trigger-based frame. The first symbol and the second symbol may be positioned in the first RU by using/based on TDMA. The second symbol may be positioned immediately after the first symbol. Additionally, the first symbol may be positioned immediately after the second symbol. Alternatively, a guard time having the size of an SIFS may exist between the first symbol and the second symbol.

That is, each of the first STA and the second STA may decode the trigger frame, so as to verify that the first RU is being used (through the S-TDMA indication information) and to verify that each STA may transmit a trigger-based frame in the first RU via S-TDMA (through the allocation information for the first RU).

The first trigger-based frame may include legacy header field, first signal field, first Short Training Field (STF), first Long Training Field (LTF), and first data field.

The legacy header field may be related to the Legacy-Short Training Field (L-STF), Legacy-Long Training Field (L-LTF), Legacy-Signal (L-SIG) field, or Repeated Legacy-Signal (RL-SIG) field being included in the HE TB PPDU. The first signal field may be related to the HE-SIG-A field being included in the HE TB PPDU. The first STF may be related to the HE-STF being included in the HE TB PPDU, and the first LFT may be related to the HE-LTF being included in the HE TB PPDU.

In case the second trigger-based frame is transmitted after the first trigger-based frame, the second trigger-based frame may have the following structure.

The second trigger-based frame may include second STF, second LTF, and second data frame, or the second trigger-based frame may include second LTF and second data frame, or the second trigger-based frame may include only a second data frame. That is, since common information, such as the legacy header field, first signal field, and so on, are included in the first trigger-based frame, a subfield of the second trigger-based frame may be omitted. The second STF and the second LTF may be configured for the second STA.

The AP may transmit Multi Block Ack (BA) may be transmitted to the first STA and second STA. The Multi BA may receive the first and second trigger-based frames and may be transmitted after the remaining packet length and Short Inter Frame Space (SIFS).

The trigger frame may include a length field including information on a total packet length that can transmit the first and second trigger-based frames. The remaining packet length may be determined based on the length field, the first symbol offset information, and the second symbol offset information.

Additionally, a guard time may exist between the first trigger-based frame and the second trigger-based frame. The guard time may be configured as an SIFS.

Hereinafter, a case where channel sensing for an S-TDMA TB PPDU is being applied will be described.

In case the guard time is equal to or longer than a CS duration performing channel sensing (CS), if a channel is Idle during the CS duration, the second trigger-based frame may be transmitted, and, if the channel is Busy during the CS duration, the second trigger-based frame may not be transmitted. That is, regardless of the transmission or non-transmission of the first trigger-based frame, which is previously transmitted, as long as the channel is Idle, the second STA may transmit the second trigger-based frame.

In case the guard time is shorter than a CS duration performing channel sensing (CS), if a channel is Busy during the CS duration, the second trigger-based frame may be transmitted, and, if the channel is Idle during the CS duration, the second trigger-based frame may not be transmitted. That is, depending upon the transmission or non-transmission of the first trigger-based frame, which is previously transmitted, the second STA transmits the second trigger-based frame only in case the first trigger-based frame is transmitted (in case the channel is Busy).

The AP may transmit the trigger frame to a third STA. The AP may receive a third trigger-based frame from the third STA.

The user information field may further include allocation information for a second RU from which the third trigger-based frame is to be transmitted. The third trigger-based frame may be transmitted in the second RU based on the allocation information for the second RU. The first RU and the second RU may be different frequency bands. That is, the third data field indicates that it may be received based on OFDMA.

According to the above-described method, by time-dividing one RU and allocating the time-divided RU to multiple STAs, waste of resource may be reduced.

This specification proposes a scheme for transmitting/receiving a PPDU based on S-TDMA in a wireless LAN system.

According to the embodiments proposed in this specification, by generating a PPDU configured of fields being newly defined based on S-TDMA, and by performing time-division on one RU and allocating the time-divided RU to multiple STAs, waste of resources may be reduced.

FIG. 1 is a conceptual view illustrating the structure of a wireless local area network (WLAN).

An upper part of FIG. 1 illustrates the structure of an infrastructure basic service set (BSS) of institute of electrical and electronic engineers (IEEE) 802.11.

Referring the upper part of FIG. 1, the wireless LAN system may include one or more infrastructure BSSs (100, 105) (hereinafter, referred to as BSS). The BSSs (100, 105), as a set of an AP and an STA such as an access point (AP) (125) and a station (STA1) (100-1) which are successfully synchronized to communicate with each other, are not concepts indicating a specific region. The BSS (105) may include one or more STAs (105-1, 105-2) which may be joined to one AP (130).

The BSS may include at least one STA, APs providing a distribution service, and a distribution system (DS) (110) connecting multiple APs.

The distribution system (110) may implement an extended service set (ESS) (140) extended by connecting the multiple BSSs (100, 105). The ESS (140) may be used as a term indicating one network configured by connecting one or more APs (125, 130) through the distribution system (110). The AP included in one ESS (140) may have the same service set identification (SSID).

A portal (120) may serve as a bridge which connects the wireless LAN network (IEEE 802.11) and another network (e.g., 802.X).

In the BSS illustrated in the upper part of FIG. 1, a network between the APs (125, 130) and a network between the APs (125, 130) and the STAs (100-1, 105-1, 105-2) may be implemented. However, the network is configured even between the STAs without the APs (125, 130) to perform communication. A network in which the communication is performed by configuring the network even between the STAs without the APs (125, 130) is defined as an Ad-Hoc network or an independent basic service set (IBSS).

A lower part of FIG. 1 illustrates a conceptual view illustrating the IBSS.

Referring to the lower part of FIG. 1, the IBSS is a BSS that operates in an Ad-Hoc mode. Since the IBSS does not include the access point (AP), a centralized management entity that performs a management function at the center does not exist. That is, in the IBSS, STAs (150-1, 150-2, 150-3, 155-4, 155-5) are managed by a distributed manner. In the IBS S, all STAs (150-1, 150-2, 150-3, 155-4, 155-5) may be constituted by movable STAs and are not permitted to access the DS to constitute a self-contained network.

The STA as a predetermined functional medium that includes a medium access control (MAC) that follows a regulation of an Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard and a physical layer interface for a radio medium may be used as a meaning including all of the APs and the non-AP stations (STAs).

The STA may be called various a name such as a mobile terminal, a wireless device, a wireless transmit/receive unit (WTRU), user equipment (UE), a mobile station (MS), a mobile subscriber unit, or just a user.

Meanwhile, the term user may be used in various meanings, for example, in wireless LAN communication, this term may be used to signify a STA participating in uplink MU MIMO and/or uplink OFDMA transmission. However, the meaning of this term will not be limited only to this.

FIG. 2 is a diagram illustrating an example of a PPDU used in an IEEE standard.

As illustrated in FIG. 2, various types of PHY protocol data units (PPDUs) may be used in a standard such as IEEE a/g/n/ac, and so on. In detail, LTF and STF fields include a training signal, SIG-A and SIG-B include control information for a receiving station, and a data field includes user data corresponding to a PSDU.

In the embodiment, an improved technique is provided, which is associated with a signal (alternatively, a control information field) used for the data field of the PPDU. The signal provided in the embodiment may be applied onto high efficiency PPDU (HE PPDU) according to an IEEE 802.11ax standard. That is, the signal improved in the embodiment may be HE-SIG-A and/or HE-SIG-B included in the HE PPDU. The HE-SIG-A and the HE-SIG-B may be represented even as the SIG-A and SIG-B, respectively. However, the improved signal proposed in the embodiment is not particularly limited to an HE-SIG-A and/or HE-SIG-B standard and may be applied to control/data fields having various names, which include the control information in a wireless communication system transferring the user data.

FIG. 3 is a diagram illustrating an example of an HE PDDU.

The control information field provided in the embodiment may be the HE-SIG-B included in the HE PPDU. The HE PPDU according to FIG. 3 is one example of the PPDU for multiple users and only the PPDU for the multiple users may include the HE-SIG-B and the corresponding HE SIG-B may be omitted in a PPDU for a single user.

As illustrated in FIG. 3, the HE-PPDU for multiple users (MUs) may include a legacy-short training field (L-STF), a legacy-long training field (L-LTF), a legacy-signal (L-SIG), a high efficiency-signal A (HE-SIG A), a high efficiency-signal-B (HE-SIG B), a high efficiency-short training field (HE-STF), a high efficiency-long training field (HE-LTF), a data field (alternatively, an MAC payload), and a packet extension (PE) field. The respective fields may be transmitted during an illustrated time period (that is, 4 or 8 μs).

More detailed description of the respective fields of FIG. 3 will be made below.

FIG. 4 is a diagram illustrating a layout of resource units (RUs) used in a band of 20 MHz.

As illustrated in FIG. 4, resource units (RUs) corresponding to tone (that is, subcarriers) of different numbers are used to constitute some fields of the HE-PPDU. For example, the resources may be allocated by the unit of the RU illustrated for the HE-STF, the HE-LTF, and the data field.

As illustrated in an uppermost part of FIG. 4, 26 units (that is, units corresponding to 26 tones). 6 tones may be used as a guard band in a leftmost band of the 20 MHz band and 5 tones may be used as the guard band in a rightmost band of the 20 MHz band. Further, 7 DC tones may be inserted into a center band, that is, a DC band and a 26-unit corresponding to each 13 tones may be present at left and right sides of the DC band. The 26-unit, a 52-unit, and a 106-unit may be allocated to other bands. Each unit may be allocated for a receiving station, that is, a user.

Meanwhile, the RU layout of FIG. 4 may be used even in a situation for a single user (SU) in addition to the multiple users (MUs) and, in this case, as illustrated in a lowermost part of FIG. 4, one 242-unit may be used and, in this case, three DC tones may be inserted.

In one example of FIG. 4, RUs having various sizes, that is, a 26-RU, a 52-RU, a 106-RU, a 242-RU, and the like are proposed, and as a result, since detailed sizes of the RUs may extend or increase, the embodiment is not limited to a detailed size (that is, the number of corresponding tones) of each RU.

FIG. 5 is a diagram illustrating a layout of resource units (RUs) used in a band of 40 MHz.

Similarly to a case in which the RUs having various RUs are used in one example of FIG. 4, 26-RU, 52-RU, 106-RU, 242-RU, 484-RU, and the like, may be used even in one example of FIG. 5. Further, 5 DC tones may be inserted into a center frequency, 12 tones may be used as the guard band in the leftmost band of the 40 MHz band and 11 tones may be used as the guard band in the rightmost band of the 40 MHz band.

In addition, as illustrated in FIG. 5, when the RU layout is used for the single user, the 484-RU may be used. That is, the detailed number of RUs may be modified similarly to one example of FIG. 4.

FIG. 6 is a diagram illustrating a layout of resource units (RUs) used in a band of 80 MHz.

Similarly to a case in which the RUs having various RUs are used in one example of each of FIG. 4 or 5, 26-RU, 52-RU, 106-RU, 242-RU, 484-RU, and the like, may be used even in one example of FIG. 6. Further, 7 DC tones may be inserted into the center frequency, 12 tones may be used as the guard band in the leftmost band of the 80 MHz band and 11 tones may be used as the guard band in the rightmost band of the 80 MHz band. In addition, the 26-RU may be used, which uses 13 tones positioned at each of left and right sides of the DC band.

Moreover, as illustrated in FIG. 6, when the RU layout is used for the single user, 996-RU may be used and, in this case, 5 DC tones may be inserted.

Meanwhile, the detailed number of RUs may be modified similarly to one example of each of FIG. 4 or FIG. 5.

FIG. 7 is a diagram illustrating another example of the HE PPDU.

A block illustrated in FIG. 7 is another example of describing the HE-PPDU block of FIG. 3 in terms of a frequency.

An illustrated L-STF (700) may include a short training orthogonal frequency division multiplexing (OFDM) symbol. The L-STF (700) may be used for frame detection, automatic gain control (AGC), diversity detection, and coarse frequency/time synchronization.

An L-LTF (710) may include a long training orthogonal frequency division multiplexing (OFDM) symbol. The L-LTF (710) may be used for fine frequency/time synchronization and channel prediction.

An L-SIG (720) may be used for transmitting control information. The L-SIG (720) may include information regarding a data rate and a data length. Further, the L-SIG (720) may be repeatedly transmitted. That is, a new format, in which the L-SIG (720) is repeated (for example, may be referred to as R-LSIG) may be configured.

An HE-SIG-A (730) may include the control information common to the receiving station.

In detail, the HE-SIG-A (730) may include information on 1) a DL/UL indicator, 2) a BSS color field indicating an identify of a BSS, 3) a field indicating a remaining time of a current TXOP period, 4) a bandwidth field indicating at least one of 20, 40, 80, 160 and 80+80 MHz, 5) a field indicating an MCS technique applied to the HE-SIG-B, 6) an indication field regarding whether the HE-SIG-B is modulated by a dual subcarrier modulation technique for MCS, 7) a field indicating the number of symbols used for the HE-SIG-B, 8) a field indicating whether the HE-SIG-B is configured for a full bandwidth MIMO transmission, 9) a field indicating the number of symbols of the HE-LTF, 10) a field indicating the length of the HE-LTF and a CP length, 11) a field indicating whether an OFDM symbol is present for LDPC coding, 12) a field indicating control information regarding packet extension (PE), and 13) a field indicating information on a CRC field of the HE-SIG-A, and the like. A detailed field of the HE-SIG-A may be added or partially omitted. Further, some fields of the HE-SIG-A may be partially added or omitted in other environments other than a multi-user (MU) environment.

In addition, the HE-SIG-A (730) may be composed of two parts: HE-SIG-A1 and HE-SIG-A2. HE-SIG-A1 and HE-SIG-A2 included in the HE-SIG-A may be defined by the following format structure (fields) according to the PPDU. First, the HE-SIG-A field of the HE SU PPDU may be defined as follows.

In addition, the HE-SIG-A field of the HE MU PPDU may be defined as follows.

In addition, the HE-SIG-A field of the HE TB PPDU may be defined as follows.

An HE-SIG-B (740) may be included only in the case of the PPDU for the multiple users (MUs) as described above. Principally, an HE-SIG-A (750) or an HE-SIG-B (760) may include resource allocation information (alternatively, virtual resource allocation information) for at least one receiving STA.

FIG. 8 is a block diagram illustrating one example of HE-SIG-B according to an embodiment.

As illustrated in FIG. 8, the HE-SIG-B field includes a common field at a frontmost part and the corresponding common field is separated from a field which follows therebehind to be encoded. That is, as illustrated in FIG. 8, the HE-SIG-B field may include a common field including the common control information and a user-specific field including user-specific control information. In this case, the common field may include a CRC field corresponding to the common field, and the like and may be coded to be one BCC block. The user-specific field subsequent thereafter may be coded to be one BCC block including the “user-specific field” for 2 users and a CRC field corresponding thereto as illustrated in FIG. 8.

A previous field of the HE-SIG-B (740) may be transmitted in a duplicated form on a MU PPDU. In the case of the HE-SIG-B (740), the HE-SIG-B (740) transmitted in some frequency band (e.g., a fourth frequency band) may even include control information for a data field corresponding to a corresponding frequency band (that is, the fourth frequency band) and a data field of another frequency band (e.g., a second frequency band) other than the corresponding frequency band. Further, a format may be provided, in which the HE-SIG-B (740) in a specific frequency band (e.g., the second frequency band) is duplicated with the HE-SIG-B (740) of another frequency band (e.g., the fourth frequency band). Alternatively, the HE-SIG B (740) may be transmitted in an encoded form on all transmission resources. A field after the HE-SIG B (740) may include individual information for respective receiving STAs receiving the PPDU.

The HE-STF (750) may be used for improving automatic gain control estimation in a multiple input multiple output (MIMO) environment or an OFDMA environment.

The HE-LTF (760) may be used for estimating a channel in the MIMO environment or the OFDMA environment.

The size of fast Fourier transform (FFT)/inverse fast Fourier transform (IFFT) applied to the HE-STF (750) and the field after the HE-STF (750), and the size of the FFT/IFFT applied to the field before the HE-STF (750) may be different from each other. For example, the size of the FFT/IFFT applied to the HE-STF (750) and the field after the HE-STF (750) may be four times larger than the size of the FFT/IFFT applied to the field before the HE-STF (750).

For example, when at least one field of the L-STF (700), the L-LTF (710), the L-SIG (720), the HE-SIG-A (730), and the HE-SIG-B (740) on the PPDU of FIG. 7 is referred to as a first field, at least one of the data field (770), the HE-STF (750), and the HE-LTF (760) may be referred to as a second field. The first field may include a field associated with a legacy system and the second field may include a field associated with an HE system. In this case, the fast Fourier transform (FFT) size and the inverse fast Fourier transform (IFFT) size may be defined as a size which is N (N is a natural number, e.g., N=1, 2, and 4) times larger than the FFT/IFFT size used in the legacy wireless LAN system. That is, the FFT/IFFT having the size may be applied, which is N (=4) times larger than the first field of the HE PPDU. For example, 256 FFT/IFFT may be applied to a bandwidth of 20 MHz, 512 FFT/IFFT may be applied to a bandwidth of 40 MHz, 1024 FFT/IFFT may be applied to a bandwidth of 80 MHz, and 2048 FFT/IFFT may be applied to a bandwidth of continuous 160 MHz or discontinuous 160 MHz.

In other words, a subcarrier space/subcarrier spacing may have a size which is 1/N times (N is the natural number, e.g., N=4, the subcarrier spacing is set to 78.125 kHz) the subcarrier space used in the legacy wireless LAN system. That is, subcarrier spacing having a size of 312.5 kHz, which is legacy subcarrier spacing may be applied to the first field of the HE PPDU and a subcarrier space having a size of 78.125 kHz may be applied to the second field of the HE PPDU.

Alternatively, an IDFT/DFT period applied to each symbol of the first field may be expressed to be N (=4) times shorter than the IDFT/DFT period applied to each data symbol of the second field. That is, the IDFT/DFT length applied to each symbol of the first field of the HE PPDU may be expressed as 3.2 μs and the IDFT/DFT length applied to each symbol of the second field of the HE PPDU may be expressed as 3.2 μs*4 (=12.8 μs). The length of the OFDM symbol may be a value acquired by adding the length of a guard interval (GI) to the IDFT/DFT length. The length of the GI may have various values such as 0.4 ρs, 0.8 ρs, 1.6 ρs, 2.4 ρs, and 3.2 ρs.

For simplicity in the description, in FIG. 7, it is expressed that a frequency band used by the first field and a frequency band used by the second field accurately coincide with each other, but both frequency bands may not completely coincide with each other, in actual. For example, a primary band of the first field (L-STF, L-LTF, L-SIG, HE-SIG-A, and HE-SIG-B) corresponding to the first frequency band may be the same as the most portions of a frequency band of the second field (HE-STF, HE-LTF, and Data), but boundary surfaces of the respective frequency bands may not coincide with each other. As illustrated in FIGS. 4 to 6, since multiple null subcarriers, DC tones, guard tones, and the like are inserted during arranging the RUs, it may be difficult to accurately adjust the boundary surfaces.

The user (e.g., a receiving station) may receive the HE-SIG-A (730) and may be instructed to receive the downlink PPDU based on the HE-SIG-A (730). In this case, the STA may perform decoding based on the FFT size changed from the HE-STF (750) and the field after the HE-STF (750). On the contrary, when the STA may not be instructed to receive the downlink PPDU based on the HE-SIG-A (730), the STA may stop the decoding and configure a network allocation vector (NAV). A cyclic prefix (CP) of the HE-STF (750) may have a larger size than the CP of another field and the during the CP period, the STA may perform the decoding for the downlink PPDU by changing the FFT size.

Hereinafter, in the embodiment of the present disclosure, data (alternatively, or a frame) which the AP transmits to the STA may be expressed as a terms called downlink data (alternatively, a downlink frame) and data (alternatively, a frame) which the STA transmits to the AP may be expressed as a term called uplink data (alternatively, an uplink frame). Further, transmission from the AP to the STA may be expressed as downlink transmission and transmission from the STA to the AP may be expressed as a term called uplink transmission.

In addition, a PHY protocol data unit (PPDU), a frame, and data transmitted through the downlink transmission may be expressed as terms such as a downlink PPDU, a downlink frame, and downlink data, respectively. The PPDU may be a data unit including a PPDU header and a physical layer service data unit (PSDU) (alternatively, a MAC protocol data unit (MPDU)). The PPDU header may include a PHY header and a PHY preamble and the PSDU (alternatively, MPDU) may include the frame or indicate the frame (alternatively, an information unit of the MAC layer) or be a data unit indicating the frame. The PHY header may be expressed as a physical layer convergence protocol (PLCP) header as another term and the PHY preamble may be expressed as a PLCP preamble as another term.

Further, a PPDU, a frame, and data transmitted through the uplink transmission may be expressed as terms such as an uplink PPDU, an uplink frame, and uplink data, respectively.

In the wireless LAN system to which the embodiment of the present description is applied, the total bandwidth may be used for downlink transmission to one STA and uplink transmission to one STA. Further, in the wireless LAN system to which the embodiment of the present description is applied, the AP may perform downlink (DL) multi-user (MU) transmission based on multiple input multiple output (MU MIMO) and the transmission may be expressed as a term called DL MU MIMO transmission.

In addition, in the wireless LAN system according to the embodiment, an orthogonal frequency division multiple access (OFDMA) based transmission method is preferably supported for the uplink transmission and/or downlink transmission. That is, data units (e.g., RUs) corresponding to different frequency resources are allocated to the user to perform uplink/downlink communication. In detail, in the wireless LAN system according to the embodiment, the AP may perform the DL MU transmission based on the OFDMA and the transmission may be expressed as a term called DL MU OFDMA transmission. When the DL MU OFDMA transmission is performed, the AP may transmit the downlink data (alternatively, the downlink frame and the downlink PPDU) to the plurality of respective STAs through the plurality of respective frequency resources on an overlapped time resource. The plurality of frequency resources may be a plurality of subbands (alternatively, subchannels) or a plurality of resource units (RUs). The DL MU OFDMA transmission may be used together with the DL MU MIMO transmission. For example, the DL MU MIMO transmission based on a plurality of space-time streams (alternatively, spatial streams) may be performed on a specific subband (alternatively, subchannel) allocated for the DL MU OFDMA transmission.

Further, in the wireless LAN system according to the embodiment, uplink multi-user (UL MU) transmission in which the plurality of STAs transmits data to the AP on the same time resource may be supported. Uplink transmission on the overlapped time resource by the plurality of respective STAs may be performed on a frequency domain or a spatial domain.

When the uplink transmission by the plurality of respective STAs is performed on the frequency domain, different frequency resources may be allocated to the plurality of respective STAs as uplink transmission resources based on the OFDMA. The different frequency resources may be different subbands (alternatively, subchannels) or different resources units (RUs). The plurality of respective STAs may transmit uplink data to the AP through different frequency resources. The transmission method through the different frequency resources may be expressed as a term called a UL MU OFDMA transmission method.

When the uplink transmission by the plurality of respective STAs is performed on the spatial domain, different time-space streams (alternatively, spatial streams) may be allocated to the plurality of respective STAs and the plurality of respective STAs may transmit the uplink data to the AP through the different time-space streams. The transmission method through the different spatial streams may be expressed as a term called a UL MU MIMO transmission method.

The UL MU OFDMA transmission and the UL MU MIMO transmission may be used together with each other. For example, the UL MU MIMO transmission based on the plurality of space-time streams (alternatively, spatial streams) may be performed on a specific subband (alternatively, subchannel) allocated for the UL MU OFDMA transmission.

In the legacy wireless LAN system which does not support the MU OFDMA transmission, a multi-channel allocation method is used for allocating a wider bandwidth (e.g., a 20 MHz excess bandwidth) to one terminal. When a channel unit is 20 MHz, multiple channels may include a plurality of 20 MHz-channels. In the multi-channel allocation method, a primary channel rule is used to allocate the wider bandwidth to the terminal. When the primary channel rule is used, there is a limit for allocating the wider bandwidth to the terminal. In detail, according to the primary channel rule, when a secondary channel adjacent to a primary channel is used in an overlapped BSS (OBSS) and is thus busy, the STA may use remaining channels other than the primary channel. Therefore, since the STA may transmit the frame only to the primary channel, the STA receives a limit for transmission of the frame through the multiple channels. That is, in the legacy wireless LAN system, the primary channel rule used for allocating the multiple channels may be a large limit in obtaining a high throughput by operating the wider bandwidth in a current wireless LAN environment in which the OBSS is not small.

In order to solve the problem, in the embodiment, a wireless LAN system is disclosed, which supports the OFDMA technology. That is, the OFDMA technique may be applied to at least one of downlink and uplink. Further, the MU-MIMO technique may be additionally applied to at least one of downlink and uplink. When the OFDMA technique is used, the multiple channels may be simultaneously used by not one terminal but multiple terminals without the limit by the primary channel rule. Therefore, the wider bandwidth may be operated to improve efficiency of operating a wireless resource.

As described above, in case the uplink transmission performed by each of the multiple STAs (e.g., non-AP STAs) is performed within the frequency domain, the AP may allocate different frequency resources respective to each of the multiple STAs as uplink transmission resources based on OFDMA. Additionally, as described above, the frequency resources each being different from one another may correspond to different subbands (or sub-channels) or different resource units (RUs).

The different frequency resources respective to each of the multiple STAs are indicated through a trigger frame.

FIG. 9 illustrates an example of a trigger frame. The trigger frame of FIG. 9 allocates resources for Uplink Multiple-User (MU) transmission and may be transmitted from the AP. The trigger frame may be configured as a MAC frame and may be included in the PPDU. For example, the trigger frame may be transmitted through the PPDU shown in FIG. 3, through the legacy PPDU shown in FIG. 2, or through a certain PPDU, which is newly designed for the corresponding trigger frame. In case the trigger frame is transmitted through the PPDU of FIG. 3, the trigger frame may be included in the data field shown in the drawing.

Each of the fields shown in FIG. 9 may be partially omitted, or other fields may be added. Moreover, the length of each field may be varied differently as shown in the drawing.

A Frame Control field (910) shown in FIG. 9 may include information related to a version of the MAC protocol and other additional control information, and a Duration field (920) may include time information for configuring a NAV or information related to an identifier (e.g., AID) of the user equipment.

Also, the RA field (930) includes address information of a receiving STA of the corresponding trigger frame and may be omitted if necessary. The TA field (940) includes address information of an STA triggering the corresponding trigger frame (for example, an AP), and the common information field (950) includes common control information applied to a receiving STA that receives the corresponding trigger frame. For example, a field indicating the length of the L-SIG field of the UL PPDU transmitted in response to the corresponding trigger frame or information controlling the content of the SIG-A field (namely, the HE-SIG-A field) of the UL PPDU transmitted in response to the corresponding trigger frame may be included. Also, as common control information, information on the length of the CP of the UP PPDU transmitted in response to the corresponding trigger frame or information on the length of the LTF field may be included.

Also, it is preferable to include a per user information field (960 #1 to 960 #N) corresponding to the number of receiving STAs that receive the trigger frame of FIG. 9. The per user information field may be referred to as an “RU allocation field”.

Also, the trigger frame of FIG. 9 may include a padding field (970) and a frame check sequence field (980).

It is preferable that each of the per user information fields (960 #1 to 960 #N) shown in FIG. 9 includes a plurality of subfields.

FIG. 10 illustrates an example of a common information field. Among the subfields of FIG. 10, some may be omitted, and other additional subfields may also be added. Additionally, the length of each of the subfields shown in the drawing may be varied.

The trigger type field (1010) of FIG. 10 may indicate a trigger frame variant and encoding of the trigger frame variant. The trigger type field (1010) may be defined as follows.

The UL BW field (1020) of FIG. 10 indicates bandwidth in the HE-SIG-A field of an HE Trigger Based (TB) PPDU. The UL BW field (1020) may be defined as follows.

The Guard Interval (GI) and LTF type fields (1030) of FIG. 10 indicate the GI and HE-LTF type of the HE TB PPDU response. The GI and LTF type field (1030) may be defined as follows.

Also, when the GI and LTF type fields (1030) have a value of 2 or 3, the MU-MIMO LTF mode field (1040) of FIG. 10 indicates the LTF mode of a UL MU-MIMO HE TB PPDU response. At this time, the MU-MIMO LTF mode field (1040) may be defined as follows.

If the trigger frame allocates an RU that occupies the whole HE TB PPDU bandwidth and the RU is allocated to one or more STAs, the MU-MIMO LTF mode field (1040) indicates one of an HE single stream pilot HE-LTF mode or an HE masked HE-LTF sequence mode.

If the trigger frame does not allocate an RU that occupies the whole HE TB PPDU bandwidth and the RU is not allocated to one or more STAs, the MU-MIMO LTF mode field (1040) indicates the HE single stream pilot HE-LTF mode. The MU-MIMO LTF mode field (1040) may be defined as follows.

FIG. 11 illustrates an example of a subfield being included in a per user information field. Among the subfields of FIG. 11, some may be omitted, and other additional subfields may also be added. Additionally, the length of each of the subfields shown in the drawing may be varied.

The User Identifier field of FIG. 11 (or AID12 field, 1110) indicates the identifier of an STA (namely, a receiving STA) corresponding to per user information, where an example of the identifier may be the whole or part of the AID.

Also, an RU Allocation field (1120) may be included. In other words, when a receiving STA identified by the User Identifier field (1110) transmits a UL PPDU in response to the trigger frame of FIG. 9, the corresponding UL PPDU is transmitted through an RU indicated by the RU Allocation field (1120). In this case, it is preferable that the RU indicated by the RU Allocation field (1120) indicates the RUs shown in FIGS. 4, 5, and 6. A specific structure of the RU Allocation field (1120) will be described later.

The subfield of FIG. 11 may include a (UL FEC) coding type field (1130). The coding type field (1130) may indicate the coding type of an uplink PPDU transmitted in response to the trigger frame of FIG. 9. For example, when BCC coding is applied to the uplink PPDU, the coding type field (1130) may be set to ‘1’, and when LDPC coding is applied, the coding type field (1130) may be set to ‘0’.

Additionally, the subfield of FIG. 11 may include a UL MCS field (1140). The MCS field (1140) may indicate an MCS scheme being applied to the uplink PPDU that is transmitted in response to the trigger frame of FIG. 9.

Also, the subfield of FIG. 11 may include a Trigger Dependent User Info field (1150). When the Trigger Type field (1010) of FIG. 10 indicates a basic trigger variant, the Trigger Dependent User Info field (1150) may include an MPDU MU Spacing Factor subfield (2 bits), a TID Aggregate Limit subfield (3 bits), a Reserved field (1 bit), and a Preferred AC subfield (2 bits).

Hereinafter, the present disclosure proposes an example of improving a control field included in a PPDU. The control field improved according to the present disclosure includes a first control field including control information required to interpret the PPDU and a second control field including control information for demodulate the data field of the PPDU. The first and second control fields may be used for various fields. For example, the first control field may be the HE-SIG-A (730) of FIG. 7, and the second control field may be the HE-SIG-B (740) shown in FIGS. 7 and 8.

Hereinafter, a specific example of improving the first or the second control field will be described.

In the following example, a control identifier inserted to the first control field or a second control field is proposed. The size of the control identifier may vary, which, for example, may be implemented with 1-bit information.

The control identifier (for example, a 1-bit identifier) may indicate whether a 242-type RU is allocated when, for example, 20 MHz transmission is performed. As shown in FIGS. 4 to 6, RUs of various sizes may be used. These RUs may be divided broadly into two types. For example, all of the RUs shown in FIGS. 4 to 6 may be classified into 26-type RUs and 242-type RUs. For example, a 26-type RU may include a 26-RU, a 52-RU, and a 106-RU while a 242-type RU may include a 242-RU, a 484-RU, and a larger RU.

The control identifier (for example, a 1-bit identifier) may indicate that a 242-type RU has been used. In other words, the control identifier may indicate that a 242-RU, a 484-RU, or a 996-RU is included. If the transmission frequency band in which a PPDU is transmitted has a bandwidth of 20 MHz, a 242-RU is a single RU corresponding to the full bandwidth of the transmission frequency band (namely, 20 MHz). Accordingly, the control identifier (for example, 1-bit identifier) may indicate whether a single RU corresponding to the full bandwidth of the transmission frequency band is allocated.

For example, if the transmission frequency band has a bandwidth of 40 MHz, the control identifier (for example, a 1-bit identifier) may indicate whether a single RU corresponding to the full bandwidth (namely, bandwidth of 40 MHz) of the transmission frequency band has been allocated. In other words, the control identifier may indicate whether a 484-RU has been allocated for transmission in the frequency band with a bandwidth of 40 MHz.

For example, if the transmission frequency band has a bandwidth of 80 MHz, the control identifier (for example, a 1-bit identifier) may indicate whether a single RU corresponding to the full bandwidth (namely, bandwidth of 80 MHz) of the transmission frequency band has been allocated. In other words, the control identifier may indicate whether a 996-RU has been allocated for transmission in the frequency band with a bandwidth of 80 MHz.

Various technical effects may be achieved through the control identifier (for example, 1-bit identifier).

First of all, when a single RU corresponding to the full bandwidth of the transmission frequency band is allocated through the control identifier (for example, a 1-bit identifier), allocation information of the RU may be omitted. In other words, since only one RU rather than a plurality of RUs is allocated over the whole transmission frequency band, allocation information of the RU may be omitted deliberately.

Also, the control identifier may be used as signaling for full bandwidth MU-MIMO. For example, when a single RU is allocated over the full bandwidth of the transmission frequency band, multiple users may be allocated to the corresponding single RU. In other words, even though signals for each user are not distinctive in the temporal and spatial domains, other techniques (for example, spatial multiplexing) may be used to multiplex the signals for multiple users in the same, single RU. Accordingly, the control identifier (for example, a 1-bit identifier) may also be used to indicate whether to use the full bandwidth MU-MIMO described above.

The common field included in the second control field (HE-SIG-B, 740) may include an RU allocation subfield. According to the PPDU bandwidth, the common field may include a plurality of RU allocation subfields (including N RU allocation subfields). The format of the common field may be defined as follows.

The RU allocation subfield included in the common field of the HE-SIG-B may be configured with 8 bits and may indicate as follows with respect to 20 MHz PPDU bandwidth. RUs to be used as a data portion in the frequency domain are allocated using an index for RU size and disposition in the frequency domain. The mapping between an 8-bit RU allocation subfield for RU allocation and the number of users per RU may be defined as follows.

The user-specific field included in the second control field (HE-SIG-B, 740) may include a user field, a CRC field, and a Tail field. The format of the user-specific field may be defined as follows.

Also, the user-specific field of the HE-SIG-B is composed of a plurality of user fields. The plurality of user fields are located after the common field of the HE-SIG-B. The location of the RU allocation subfield of the common field and that of the user field of the user-specific field are used together to identify an RU used for transmitting data of an STA. A plurality of RUs designated as a single STA are now allowed in the user-specific field. Therefore, signaling that allows an STA to decode its own data is transmitted only in one user field.

As an example, it may be assumed that the RU allocation subfield is configured with 8 bits of 01000010 to indicate that five 26-tone RUs are arranged next to one 106-tone RU and three user fields are included in the 106-tone RU. At this time, the 106-tone RU may support multiplexing of the three users. This example may indicate that eight user fields included in the user-specific field are mapped to six RUs, the first three user fields are allocated according to the MU-MIMO scheme in the first 106-tone RU, and the remaining five user fields are allocated to each of the five 26-tone RUs.

User fields included in the user-specific field of the HE-SIG-B may be defined as described below. Firstly, user fields for non-MU-MIMO allocation are as described below.

User fields for MU-MIMO allocation are as described below.

FIG. 12 illustrates an example of an HE TB PPDU. The PPDU of FIG. 12 illustrates an uplink PPDU transmitted in response to the trigger frame of FIG. 9. At least one STA receiving a trigger frame from an AP may check the common information field and the individual user information field of the trigger frame and may transmit a HE TB PPDU simultaneously with another STA which has received the trigger frame.

As shown in the figure, the PPDU of FIG. 12 includes various fields, each of which corresponds to the field shown in FIGS. 2, 3, and 7. Meanwhile, as shown in the figure, the HE TB PPDU (or uplink PPDU) of FIG. 12 may not include the HE-SIG-B field but only the HE-SIG-A field.

Although a PHY transmit/receive procedure in Wi-Fi may have different detailed packet configuration methods, the PHY transmit/receive procedure will be described as follows. For simplicity, although examples will only be presented for 11n and 11ax, 11g/ac also follows a similar procedure.

That is, in a PHY transmit procedure, when a MAC protocol data unit (MPDU) or Aggregate MPDU (A-MPDU) arrives at a MAC end, the MPDU or A-MPDU are converted to a Single PHY service data unit (PSDU), at a PHY end, and then transmitted after inserting a Preamble, Tail bits, and padding bits (if needed). This is referred to as a PPDU.

Generally, a PHY receive procedure is as described below. When energy detection and preamble detection (L/HT/VHT/HE-preamble detection per Wi-Fi version) are performed, information on a PSDU configuration is obtained (or acquired) from a PHY header (L/HT/VHT/HE-SIG), and, then, a MAC header is read, and data is read.

FIG. 13 illustrates an example of a DL MU packet being allocated to a RU, wherein the UL MU packet is transmitted by multiple STAs using 802.11 OFDMA.

FIG. 13 illustrates an example of transmitting, by an AP, a Trigger frame to multiple STAs in a legacy 802.11ax, and allocating a received OFDMA-based UL MU packet (being configured of an HE TB PPDU), i.e., multiple STA data, to an RU.

When performing OFDMA UL transmission, a UL MU packet matches its length to a Length field value of a Trigger frame, and, in case a data size, MCS, and so on, of each STA is/are different, although it may differ according to the scheduling method of the AP, as shown in FIG. 13, each packet may be filled and the remaining resource parts may be filled with padding bits. Since such padding is not used for sending data, a resource amount equivalent to the corresponding length is wasted. Therefore, the present disclosure proposes a Scheduled-Time Division Multiple Access (S-TDMA) technique enabling transmission to be performed by additionally allocating data of one or more STAs to empty parts, i.e., padding parts of the RU, when performing UL MU packet transmission using 802.11 OFDMA. S-TDMA is a technique for allocating data to the UE while additionally considering a time domain, in addition to the frequency domain, which is considered in the conventional OFDMA. That is, by time-dividing one RU and allocating the time-divided RU to multiple STAs, waste of resources may be reduced.

FIG. 14 illustrates an example of a UL MU packet being allocated to a RU by using/based on an OFDMA-based S-TDMA technique.

As shown in FIG. 14, when remaining resource, i.e., padding, occurs in a RU having a packet of STA 1 allocated thereto, a packet of STA 2 may be additionally allocated to the corresponding RU. Apart from the packet of STA 2, if there exists a packet of another STA that may be allocated to the padding, the packet may be additionally allocated to the corresponding RU. This specification proposes, in detail, a trigger frame format, a PPDU structure, an ACK transmission method, and a carrier sensing (CS) rule for supporting UL transmission by using/based on the S-TDMA technique.

2.1. Trigger Frame Structure for S-TDMA TB PPDU Transmission

In order to transmit an S-TDMA TB PPDU, a Trigger frame of the legacy 802.11ax may be used for scheduling, and in order to include information for applying S-TDMA, a Trigger frame needs to be modified.

Even if S-TDMA is applied to one RU, a Trigger frame shall indicate, at a higher priority, the application or non-application of S-TDMA (S-TDMA indication). The indication method is as follows.

1) Use B63 Bit, which is a Reserved Bit of a Common Field

• • That is, a Trigger frame of 802.11ax is used without modification, and the application of S-TDMA may be indicated by using/based on a reserved bit of a Common field.

2) Add an S-TDMA Trigger Type (Use 8-15, which are Reserved Bits)

• • Alternatively, a new Trigger type that is not defined in Table 4, which is presented above, may be defined as an S-TDMA Trigger type, and the S-TDMA Trigger type may be included in a Trigger Type subfield of the Common field.
  • In both methods, a new S-TDMA trigger frame format indication can be performed by using/based on the existing trigger frame format, without any modification, and without any additional overhead.

The trigger frame shall indicate a point where an STA being allocated from an RU applying S-TDMA transmits data (Starting Symbol offset). The indication method is as follows.

1) Add and Use a New Bit in a User Info Field

• • Although S-TDMA could be supported from the conventional 11ax format by using/based on an additional bit, an overhead equivalent to the added bit occurs.

2) Use Trigger Dependent User Info Through a S-TDMA Trigger Type Indication

• • A new S-TDMA trigger frame can be generated through Trigger type indication and a Trigger dependent field.

FIG. 15 illustrates an example of transmitting an S-TDMA TB PPDU according to a modified Trigger frame.

FIG. 15 shows an example of an S-TDMA Trigger frame. After indicating an S-TDMA Trigger type, a PPDU transmission point is indicated to the corresponding STA by using/based on a Trigger Dependent User Info field.

2.2. S-TDMA TB PPDU Structure

Although an S-TDMA TB PPDU can reuse an existing HE TB PPDU, a guard time (e.g., SIFS) may be applied between S-TDMA TB PPDUs arriving at an AP for a second time or more. Although a TB PPDU of an STA first performing transmission to the AP includes a Legacy PHY header and HE-SIG-A, since such information are common information, such information is not necessarily required to be included in the TB PPDUs of STAs being transmitted afterwards. Therefore, TB PPDUs of the remaining STAs excluding the STA first performing transmission to the AP may have the following formats.

1) S-TDMA STF (or HE STF)+S-TDMA LTF (or HE LTF)+Data

2) S-TDMA LTF (or HE LTF)+Data

3) Only Data

4) In case an RU is allocated to 20 MHz or more, 1), 2), and 3) may evidently follow the existing HE TB PPDU format.

FIG. 16 illustrates an exemplary S-TDMA MU PPDU structure in a 20 MHz band.

FIG. 16 is an example of an S-TDMA TB PPDU being transmitted in accordance with the situation of FIG. 15 in a first 52RU of the 20 MHz-based 52/52/106 RU allocation.

2.3. Acknowledgement for S-TDMA TB PPDU Transmission

The AP may receive all S-TDMA TB PPDUs from all STAs being scheduled by using/based on the trigger frame, and after an SIFS, the AP may transmit ACK. The transmission method may reuse Multi-STA Block ACK, and so on, which are used in the conventional 802.11ax. However, in case of S-TDMA, with the exception for the data being allocated in last place, since the ACK cannot be transmitted after SIFS, which is the existing rule, the Acknowledgement rule shall be partly modified. The modified rule is as follows.

• • The AP, which has transmitted a Trigger frame by applying S-TDMA, must transmit an ACK after a time period (or duration), which is equivalent to the remaining packet length being added to SIFS. The remaining packet length may be calculated from a total packet length, which is the value of a Length field of the Trigger frame, and a starting symbol offset of each STA.

2.4. CS Rule for S-TDMA TB PPDU Transmission

In 802.11ax, STAs receiving a Trigger frame determine whether or not a channel is BUSY via energy detection (ED) during an SIFS duration. If all or some of the allocated channels are BUSY, all HE TB PPDUs are not transmitted. And, if all or some of the allocated channels are IDLE, the HE TB PPDUs are transmitted. However, even if the channel was in an IDLE or BUSY state during an SIFS in one RU applying S-TDMA, among the transmitting STAs, with the exception for the STA first transmitting the data, the remaining STAs may experience different channel statuses. That is, after a first SIFS, since a transmission opportunity or conflict situation may be given, in a case where S-TDMA is applied, a CS rule for an S-TDMA TB PPDU may be partly modified. In case a distance (or gap) between S-TDMA TB PPDUs being transmitted from an RU applying S-TDMA is a Guard time, the rule may be modified as described below.

• • A Guard time and CS duration may have SIFS and PIFS, or other values.

<CS Rule 1>

1) In case the Guard time is equal to or longer than a CS duration, the STAs being allocated to the corresponding RU perform CS, so as to transmit a PPDU in case the channel is IDLE and not transmit a PPDU in case the channel is BUSY.

• • Each STA may determine whether or not to perform its own data transmission, regardless of the transmission or non-transmission of a TB PPDU, which is previously performed. However, in case a previous failure to transmit the TB PPDU is caused a Hidden node of the STA, there is a likelihood of conflict.

<CS Rule 2>

2) In case the Guard time is shorter than a CS duration, the STAs being allocated to the corresponding RU perform CS, so as to transmit a PPDU in case the channel is BUSY and not transmit a PPDU in case the channel is IDLE. Since the channel being BUSY indicates that a previous TB PPDU is currently being transmitted, a PPDU may be transmitted.

• • Since each STA may determine whether or not to perform its data transmission depending upon the transmission or non-transmission of a TB PPDU, which is previously performed, the Hidden node issue (or problem) may be resolved. However, it is difficult to determine whether the cause of the channel being BUSY is due to an interference from a neighboring node.

FIG. 17 illustrates an example of transmitting an S-TDMA TB PPDU according to CS rule 1. That is, FIG. 17 illustrates an S-TDMA TB PPDU transmission according to CS rule 1).

FIG. 17 illustrates a case where the Guard time and the CS duration are SIFS, and where the Guard time and the CS duration are the same. Therefore, after receiving a Trigger frame from the AP, according to a CS result of STA1, in case a channel is BUSY during an SIFS, a PPDU is not transmitted, and, according to a CS result of STA2, in case a channel is IDLE during an SIFS, a PPDU is transmitted.

FIG. 18 illustrates an example of transmitting an S-TDMA TB PPDU according to CS rule 2. FIG. 18 illustrates an S-TDMA TB PPDU transmission according to CS rule 2).

FIG. 18 illustrates a case where the Guard time is SIFS and the CS duration is PIFS, and where the Guard time is shorter (or smaller) than the CS duration. Therefore, after receiving a Trigger frame from the AP, according to a CS result of STA1, in case a channel is BUSY during an SIFS, a PPDU is not transmitted, and, according to a CS result of STA2, in case a channel is IDLE during a PIFS, a PPDU is not transmitted. Conversely, according to a CS result of STA2, in case a channel is BUSY during a PIFS, since this indicates that an S-TDMA TB PPDU of the previous STA1 is being transmitted, STA2 also transmits an S-TDMA TB PPDU.

Hereinafter, the above-described embodiment will be described according to a time flow with reference to FIG. 14 to FIG. 18.

FIG. 19 is a diagram illustrating a procedure for transmitting a TB PPDU based on S-TDMA according to an embodiment of the present disclosure.

S-TDMA is a technique for allocating data fields via scheduling to the RU while additionally considering TDMA in a time domain, in addition to the frequency domain considering OFDMA.

Referring to FIG. 19, the AP transmits a trigger frame to STA1 to STA3. The trigger frame includes a common information field and a user information field. The common information field includes S-TDMA indication information on that S-TDMA can be performed. The user information field includes allocation information for a first RU to which a TB PPDU (first trigger-based frame) being transmitted by STA1 and a TB PPDU (second trigger-based frame) being transmitted by STA2 are to be transmitted, allocation information for a second RU to which a TB PPDU (third trigger-based frame) being transmitted by STA3 is to be transmitted, and symbol offset information for a TB PPDU applying S-TDMA.

STA1 decodes the trigger frame so as to verify that it is using a first RU and the S-TDMA is being applied. Thus, STA1 may transmit a TB PPDU in the first RU during a first symbol.

STA2 decodes the trigger frame so as to verify that it is using a first RU and the S-TDMA is being applied. Similarly, STA2 may transmit a TB PPDU in the first RU during a second symbol. That is, a TB PPDU of STA1 is transmitted during a first symbol and a TB PPDU of STA2 is transmitted during a second symbol from the same first RU.

However, it is illustrated that STA3 applies only OFDMA. That is, STA3 decodes the trigger frame so as to verify that it is using a second RU but the S-TDMA is not applied. That is, STA3 alone is allocated with the second RU. STA3 may transmit a TB PPDU in the second RU. That is, the TB PPDU of STA1 and the TB PPDU of STA2 are transmitted in the first RU, and the TB PPDU of STA3 is transmitted in the second RU. According to FIG. 19, the TB PPDU of STA3 may be transmitted at the same time as the TB PPDU of STA1 and the TB PPDU of STA2 from different frequency bands.

Detailed description of the S-TDMA TB PPDU will be described later on with reference to FIG. 20 and FIG. 21.

FIG. 20 is a flow chart showing a procedure of transmitting, by an AP, a PPDU based on S-TDMA according to an embodiment of the present disclosure.

An example of FIG. 20 may be performed in a network environment supporting a next generation wireless LAN system. The next generation wireless LAN system is an improved wireless LAN system version of the 802.11ax system being capable of satisfying backward compatibility with the 802.11ax system.

Firstly, the terms will be defined. A trigger frame, HE TB PPDU, HE-SIG-A field, HE-STF field, and HE-LTF field may all be PPDU and fields that are defined in the 802.11ax system. S-TDMA TB PPDU, S-TDMA SIG-A field (first signal field), S-TDMA STF, and S-TDMA LTF may be PPDU and fields that are defined for performing S-TDMA in a next generation wireless LAN system. The trigger frame may be a trigger frame that is newly defined for performing S-TDMA in a next generation wireless LAN system. However, the PPDU and fields that are defined for performing S-TDMA may be generated by using/based on each subfield of the HE PPDU without any modification in order to satisfy backward compatibility with the 802.11ax system.

An example of FIG. 20 is performed in a transmitting device, and the transmitting device may correspond to an AP. A receiving device of FIG. 20 may correspond to a (non-AP STA) STA having S-TDMA capability.

In step S2010, an access point (AP) transmits a trigger frame to a first station (STA) and a second STA.

In step S2020, based on the trigger frame, the AP receives a first trigger-based frame from the first STA and receives a second trigger-based frame from the second STA. The first trigger-based frame and the second trigger-based frame may be S-TDMA TB PPDUs and may be newly defined in a next generation wireless LAN system. Additionally, the first trigger-based frame and the second trigger-based frame may be generated by using/based on a High Efficiency Trigger Based PPDU (HE TB PPDU). That is, the first trigger-based frame and the second trigger-based frame may be S-TDMA TB PPDUs being generated by reusing the HE TB PPDU.

The trigger frame includes a common information field and a user information field.

The common information field includes S-TDMA indication information on that the S-TDMA may be performed. The S-TDMA indication information may include a reserved bit within the trigger frame or may include a reserved bit within a trigger type subfield being included in the trigger frame.

The user information field includes allocation information for a first RU to which the first trigger-based frame and the second trigger-based frame are to be transmitted, a first symbol offset information for the first trigger-based frame, and a second symbol offset information for the second trigger-based frame. The first symbol offset information and the second symbol offset information may be included in a Trigger Dependent User Info field, which is included in the user field.

The first trigger-based frame is transmitted in the first RU during a first symbol, which is determined by the first symbol offset information. And, the second trigger-based frame is transmitted in the first RU during a second symbol, which is determined by the second symbol offset information.

The first symbol offset information may include information on a transmission start point (Starting Symbol offset) of the first trigger-based frame. The second symbol offset information may include information on a transmission start point (Starting Symbol offset) of the second trigger-based frame. The first symbol and the second symbol may be positioned in the first RU by using/based on TDMA. The second symbol may be positioned immediately after the first symbol. Additionally, the first symbol may be positioned immediately after the second symbol. Alternatively, a guard time having the size of an SIFS may exist between the first symbol and the second symbol.

That is, each of the first STA and the second STA may decode the trigger frame, so as to verify that the first RU is being used (through the S-TDMA indication information) and to verify that each STA may transmit a trigger-based frame in the first RU via S-TDMA (through the allocation information for the first RU).

The first trigger-based frame may include legacy header field, first signal field, first Short Training Field (STF), first Long Training Field (LTF), and first data field.

The legacy header field may be related to the Legacy-Short Training Field (L-STF), Legacy-Long Training Field (L-LTF), Legacy-Signal (L-SIG) field, or Repeated Legacy-Signal (RL-SIG) field being included in the HE TB PPDU. The first signal field may be related to the HE-SIG-A field being included in the HE TB PPDU. The first STF may be related to the HE-STF being included in the HE TB PPDU, and the first LTF may be related to the HE-LTF being included in the HE TB PPDU.

In case the second trigger-based frame is transmitted after the first trigger-based frame, the second trigger-based frame may have the following structure.

The second trigger-based frame may include second STF, second LTF, and second data frame, or the second trigger-based frame may include second LTF and second data frame, or the second trigger-based frame may include only a second data frame. That is, since common information, such as the legacy header field, first signal field, and so on, are included in the first trigger-based frame, a subfield of the second trigger-based frame may be omitted. The second STF and the second LTF may be configured for the second STA.

The AP may transmit Multi Block Ack (BA) may be transmitted to the first STA and second STA. The Multi BA may receive the first and second trigger-based frames and may be transmitted after the remaining packet length and Short Inter Frame Space (SIFS).

The trigger frame may include a length field including information on a total packet length that can transmit the first and second trigger-based frames. The remaining packet length may be determined based on the length field, the first symbol offset information, and the second symbol offset information.

Additionally, a guard time may exist between the first trigger-based frame and the second trigger-based frame. The guard time may be configured as an SIFS.

Hereinafter, a case where channel sensing for an S-TDMA TB PPDU is being applied will be described.

In case the guard time is equal to or longer than a CS duration performing channel sensing (CS), if a channel is Idle during the CS duration, the second trigger-based frame may be transmitted, and, if the channel is Busy during the CS duration, the second trigger-based frame may not be transmitted. That is, regardless of the transmission or non-transmission of the first trigger-based frame, which is previously transmitted, as long as the channel is Idle, the second STA may transmit the second trigger-based frame.

In case the guard time is shorter than a CS duration performing channel sensing (CS), if a channel is Busy during the CS duration, the second trigger-based frame may be transmitted, and, if the channel is Idle during the CS duration, the second trigger-based frame may not be transmitted. That is, depending upon the transmission or non-transmission of the first trigger-based frame, which is previously transmitted, the second STA transmits the second trigger-based frame only in case the first trigger-based frame is transmitted (in case the channel is Busy).

The AP may transmit the trigger frame to a third STA. The AP may receive a third trigger-based frame from the third STA.

The user information field may further include allocation information for a second RU from which the third trigger-based frame is to be transmitted. The third trigger-based frame may be transmitted in the second RU based on the allocation information for the second RU. The first RU and the second RU may be different frequency bands. That is, the third data field indicates that it may be received based on OFDMA.

According to the above-described method, by time-dividing one RU and allocating the time-divided RU to multiple STAB, waste of resource may be reduced.

FIG. 21 is a flow chart showing a procedure of receiving, by an STA, a PPDU based on S-TDMA according to an embodiment of the present disclosure.

An example of FIG. 21 may be performed in a network environment supporting a next generation wireless LAN system. The next generation wireless LAN system is an improved wireless LAN system version of the 802.11ax system being capable of satisfying backward compatibility with the 802.11ax system.

Firstly, the terms will be defined. A trigger frame, HE TB PPDU, HE-SIG-A field, HE-STF field, and HE-LTF field may all be PPDU and fields that are defined in the 802.11ax system. S-TDMA TB PPDU, S-TDMA SIG-A field (first signal field), S-TDMA STF, and S-TDMA LTF may be PPDU and fields that are defined for performing S-TDMA in a next generation wireless LAN system. The trigger frame may be a trigger frame that is newly defined for performing S-TDMA in a next generation wireless LAN system. However, the PPDU and fields that are defined for performing S-TDMA may be generated by using/based on each subfield of the HE PPDU without any modification in order to satisfy backward compatibility with the 802.11ax system.

An example of FIG. 21 may be performed in a receiving device, and the receiving device may correspond to a (non-AP STA) STA having S-TDMA capability. A transmitting device of FIG. 21 may correspond to an AP.

In step S2110, a first station (STA) receives a trigger frame from an access point (AP).

In step S2120, the first STA transmits a first trigger-based frame based on the trigger frame. At this point, a second trigger-based frame is transmitted by a second STA based on the trigger frame.

The first trigger frame and the second trigger frame are S-TDMA TB PPDUs and may be newly defined in a next generation wireless LAN system. Additionally, the first trigger-based frame and the second trigger-based frame may be generated by using/based on a High Efficiency Trigger Based PPDU (HE TB PPDU). That is, the trigger-based frame and the second trigger-based frame may be S-TDMA TB PPDUs generated by reusing the HE TB PPDU.

The trigger frame includes a common information field and a user information field.

The common information field includes S-TDMA indication information on that the S-TDMA may be performed. The S-TDMA indication information may include a reserved bit within the trigger frame or may include a reserved bit within a trigger type subfield being included in the trigger frame.

The user information field includes allocation information for a first RU to which the first trigger-based frame and the second trigger-based frame are to be transmitted, a first symbol offset information for the first trigger-based frame, and a second symbol offset information for the second trigger-based frame. The first symbol offset information and the second symbol offset information may be included in a Trigger Dependent User Info field, which is included in the user field.

The first trigger-based frame is transmitted in the first RU during a first symbol, which is determined by the first symbol offset information. And, the second trigger-based frame is transmitted in the first RU during a second symbol, which is determined by the second symbol offset information.

The first symbol offset information may include information on a transmission start point (Starting Symbol offset) of the first trigger-based frame. The second symbol offset information may include information on a transmission start point (Starting Symbol offset) of the second trigger-based frame. The first symbol and the second symbol may be positioned in the first RU by using/based on TDMA. The second symbol may be positioned immediately after the first symbol. Additionally, the first symbol may be positioned immediately after the second symbol. Alternatively, a guard time having the size of an SIFS may exist between the first symbol and the second symbol.

That is, each of the first STA and the second STA may decode the trigger frame, so as to verify that the first RU is being used (through the S-TDMA indication information) and to verify that each STA may transmit a trigger-based frame in the first RU via S-TDMA (through the allocation information for the first RU).

The first trigger-based frame may include legacy header field, first signal field, first Short Training Field (STF), first Long Training Field (LTF), and first data field.

The legacy header field may be related to the Legacy-Short Training Field (L-STF), Legacy-Long Training Field (L-LTF), Legacy-Signal (L-SIG) field, or Repeated Legacy-Signal (RL-SIG) field being included in the HE TB PPDU. The first signal field may be related to the HE-SIG-A field being included in the HE TB PPDU. The first STF may be related to the HE-STF being included in the HE TB PPDU, and the first LTF may be related to the HE-LTF being included in the HE TB PPDU.

In case the second trigger-based frame is transmitted after the first trigger-based frame, the second trigger-based frame may have the following structure.

The second trigger-based frame may include second STF, second LTF, and second data frame, or the second trigger-based frame may include second LTF and second data frame, or the second trigger-based frame may include only a second data frame. That is, since common information, such as the legacy header field, first signal field, and so on, are included in the first trigger-based frame, a subfield of the second trigger-based frame may be omitted. The second STF and the second LTF may be configured for the second STA.

The AP may transmit Multi Block Ack (BA) may be transmitted to the first STA and second STA. The Multi BA may receive the first and second trigger-based frames and may be transmitted after the remaining packet length and Short Inter Frame Space (SIFS).

The trigger frame may include a length field including information on a total packet length that can transmit the first and second trigger-based frames. The remaining packet length may be determined based on the length field, the first symbol offset information, and the second symbol offset information.

Additionally, a guard time may exist between the first trigger-based frame and the second trigger-based frame. The guard time may be configured as an SIFS.

Hereinafter, a case where channel sensing for an S-TDMA TB PPDU is being applied will be described.

In case the guard time is equal to or longer than a CS duration performing channel sensing (CS), if a channel is Idle during the CS duration, the second trigger-based frame may be transmitted, and, if the channel is Busy during the CS duration, the second trigger-based frame may not be transmitted. That is, regardless of the transmission or non-transmission of the first trigger-based frame, which is previously transmitted, as long as the channel is Idle, the second STA may transmit the second trigger-based frame.

In case the guard time is shorter than a CS duration performing channel sensing (CS), if a channel is Busy during the CS duration, the second trigger-based frame may be transmitted, and, if the channel is Idle during the CS duration, the second trigger-based frame may not be transmitted. That is, depending upon the transmission or non-transmission of the first trigger-based frame, which is previously transmitted, the second STA transmits the second trigger-based frame only in case the first trigger-based frame is transmitted (in case the channel is Busy).

The AP may transmit the trigger frame to a third STA. The AP may receive a third trigger-based frame from the third STA.

The user information field may further include allocation information for a second RU from which the third trigger-based frame is to be transmitted. The third trigger-based frame may be transmitted in the second RU based on the allocation information for the second RU. The first RU and the second RU may be different frequency bands. That is, the third data field indicates that it may be received based on OFDMA.

According to the above-described method, by time-dividing one RU and allocating the time-divided RU to multiple STAs, waste of resource may be reduced.

3. Device Configuration

FIG. 22 is a diagram describing a device for implementing the above-described method.

A wireless device (100) of FIG. 22 may be a transmitting device, which transmits a signal that is described in the description presented above, and a wireless device (150) may be a receiving device, which receives a signal that is described in the description presented above.

The transmitting device (100) may include a processor (110), a memory (120), and a transceiver (130), and the receiving device (150) may include a processor (160), a memory (170), and a transceiver (180). The transceiver (130, 180) transmits/receives a radio signal and may be operated in a physical layer of IEEE 802.11/3GPP, and so on. The processor (110, 160) may be operated in the physical layer and/or MAC layer and may be operatively connected to the transmitting/receiving unit (130, 180).

The processor (110, 160) and/or the transceiver (130, 180) may include application-specific integrated circuit (ASIC), other chipset, logic circuit and/or data processor. The memory (120, 170) may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium and/or other storage unit. When the embodiments are executed by software, the techniques (or methods) described herein can be executed with modules (e.g., processes, functions, and so on) that perform the functions described herein. The modules can be stored in the memory (120, 170) and executed by the processor (110, 160). The memory (120, 170) can be implemented (or positioned) within the processor (110, 160) or external to the processor (110, 160). Also, the memory (120, 170) may be operatively connected to the processor (110, 160) via various means known in the art.

The processor (110, 160) may implement the functions, processes and/or methods proposed in the present disclosure. For example, the processor (110, 160) may perform the operation according to the present embodiment.

Detailed operations of the processor (110) of the transmitting device are as follows. The processor (110) of the transmitting device transmits a trigger frame to a first station (STA) and a second STA, and the processor (110) of the transmitting device receives a first trigger-based frame from the first STA and receives a second trigger-based frame from the second STA.

Detailed operations of the processor (160) of the receiving device are as follows. The processor (160) of the receiving device receives a trigger frame from an access point (AP) and transmits a first trigger-based frame based on the trigger frame.

FIG. 23 illustrates a more detailed wireless device for implementing the embodiment of the present disclosure.

A wireless device includes a processor (610), a power management module (611), a battery (612), a display (613), a keypad (614), a subscriber identification module (SIM) card (615), a memory (620), a transceiver (630), one or more antennas (631), a speaker (640), and a microphone (641).

The processor (610) may be configured to implement proposed functions, procedures and/or methods of the present disclosure that are described below. Layers of the radio interface protocol may be implemented in the processor (610). The processor (610) may include application-specific integrated circuit (ASIC), other chipset, logic circuit and/or data processing device. The processor (610) may be an application processor (AP). The processor (610) may include at least one of a digital signal processor (DSP), a central processing unit (CPU), a graphics processing unit (GPU), a modem (modulator and demodulator). An example of the processor (610) may be found in SNAPDRAGON™ series of processors made by Qualcomm®, EXYNOS™ series of processors made by Samsung®, A series of processors made by Apple®, HELIO™ series of processors made by MediaTek®, ATOM™ series of processors made by Intel® or a corresponding next generation processor.

The power management module (611) manages power for the processor (610) and/or the transceiver (630). The battery (612) supplies power to the power management module (611). The display (613) outputs results processed by the processor (610). The keypad (614) receives inputs to be used by the processor (610). The keypad (614) may be shown on the display (613). The SIM card (615) is an integrated circuit that is intended to securely store the international mobile subscriber identity (IMSI) number and its related key, which are used to identify and authenticate subscribers on mobile telephony devices (such as mobile phones and computers). It is also possible to store contact information on many SIM cards.

The memory (620) is operatively coupled with the processor (610) and stores a variety of information to operate the processor (610). The memory (620) may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium and/or other storage device. When the embodiments are implemented in software, the techniques described herein may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The modules may be stored in the memory (620) and executed by the processor (610). The memory (620) may be implemented within the processor (610) or external to the processor (610) in which case those can be communicatively coupled to the processor (610) via various means as is known in the art.

The transceiver (630) is operatively coupled with the processor (610) and transmits and/or receives a radio signal. The transceiver (630) includes a transmitter and a receiver. The transceiver (630) may include baseband circuitry to process radio frequency signals. The transceiver (630) controls the one or more antennas (631) to transmit and/or receive a radio signal.

The speaker (640) outputs sound-related results processed by the processor (610). The microphone (641) receives sound-related inputs to be used by the processor (610).

In case of the transmitting device, the processor (610) of the transmitting device transmits a trigger frame to a first station (STA) and a second STA, and the processor (610) of the transmitting device receives a first trigger-based frame from the first STA and receives a second trigger-based frame from the second STA.

In case of the receiving device, the processor (160) of the receiving device receives a trigger frame from an access point (AP) and transmits a first trigger-based frame based on the trigger frame.

The first trigger-based frame and the second trigger-based frame may be S-TDMA TB PPDUs and may be newly defined in a next generation wireless LAN system. Additionally, the first trigger-based frame and the second trigger-based frame may be generated by using/based on a High Efficiency Trigger Based PPDU (HE TB PPDU). That is, the first trigger-based frame and the second trigger-based frame may be S-TDMA TB PPDUs being generated by reusing the HE TB PPDU.

The trigger frame includes a common information field and a user information field.

The common information field includes S-TDMA indication information on that the S-TDMA may be performed. The S-TDMA indication information may include a reserved bit within the trigger frame or may include a reserved bit within a trigger type subfield being included in the trigger frame.

The user information field includes allocation information for a first RU to which the first trigger-based frame and the second trigger-based frame are to be transmitted, a first symbol offset information for the first trigger-based frame, and a second symbol offset information for the second trigger-based frame. The first symbol offset information and the second symbol offset information may be included in a Trigger Dependent User Info field, which is included in the user field.

The first trigger-based frame is transmitted in the first RU during a first symbol, which is determined by the first symbol offset information. And, the second trigger-based frame is transmitted in the first RU during a second symbol, which is determined by the second symbol offset information.

The first symbol offset information may include information on a transmission start point (Starting Symbol offset) of the first trigger-based frame. The second symbol offset information may include information on a transmission start point (Starting Symbol offset) of the second trigger-based frame. The first symbol and the second symbol may be positioned in the first RU by using/based on TDMA. The second symbol may be positioned immediately after the first symbol. Additionally, the first symbol may be positioned immediately after the second symbol. Alternatively, a guard time having the size of an SIFS may exist between the first symbol and the second symbol.

That is, each of the first STA and the second STA may decode the trigger frame, so as to verify that the first RU is being used (through the S-TDMA indication information) and to verify that each STA may transmit a trigger-based frame in the first RU via S-TDMA (through the allocation information for the first RU).

The first trigger-based frame may include legacy header field, first signal field, first Short Training Field (STF), first Long Training Field (LTF), and first data field.

The legacy header field may be related to the Legacy-Short Training Field (L-STF), Legacy-Long Training Field (L-LTF), Legacy-Signal (L-SIG) field, or Repeated Legacy-Signal (RL-SIG) field being included in the HE TB PPDU. The first signal field may be related to the HE-SIG-A field being included in the HE TB PPDU. The first STF may be related to the HE-STF being included in the HE TB PPDU, and the first LTF may be related to the HE-LTF being included in the HE TB PPDU.

In case the second trigger-based frame is transmitted after the first trigger-based frame, the second trigger-based frame may have the following structure.

The second trigger-based frame may include second STF, second LTF, and second data frame, or the second trigger-based frame may include second LTF and second data frame, or the second trigger-based frame may include only a second data frame. That is, since common information, such as the legacy header field, first signal field, and so on, are included in the first trigger-based frame, a subfield of the second trigger-based frame may be omitted. The second STF and the second LTF may be configured for the second STA.

The AP may transmit Multi Block Ack (BA) may be transmitted to the first STA and second STA. The Multi BA may receive the first and second trigger-based frames and may be transmitted after the remaining packet length and Short Inter Frame Space (SIFS).

The trigger frame may include a length field including information on a total packet length that can transmit the first and second trigger-based frames. The remaining packet length may be determined based on the length field, the first symbol offset information, and the second symbol offset information.

Additionally, a guard time may exist between the first trigger-based frame and the second trigger-based frame. The guard time may be configured as an SIFS.

Hereinafter, a case where channel sensing for an S-TDMA TB PPDU is being applied will be described.

In case the guard time is equal to or longer than a CS duration performing channel sensing (CS), if a channel is Idle during the CS duration, the second trigger-based frame may be transmitted, and, if the channel is Busy during the CS duration, the second trigger-based frame may not be transmitted. That is, regardless of the transmission or non-transmission of the first trigger-based frame, which is previously transmitted, as long as the channel is Idle, the second STA may transmit the second trigger-based frame.

In case the guard time is shorter than a CS duration performing channel sensing (CS), if a channel is Busy during the CS duration, the second trigger-based frame may be transmitted, and, if the channel is Idle during the CS duration, the second trigger-based frame may not be transmitted. That is, depending upon the transmission or non-transmission of the first trigger-based frame, which is previously transmitted, the second STA transmits the second trigger-based frame only in case the first trigger-based frame is transmitted (in case the channel is Busy).

The AP may transmit the trigger frame to a third STA. The AP may receive a third trigger-based frame from the third STA.

The user information field may further include allocation information for a second RU from which the third trigger-based frame is to be transmitted. The third trigger-based frame may be transmitted in the second RU based on the allocation information for the second RU. The first RU and the second RU may be different frequency bands. That is, the third data field indicates that it may be received based on OFDMA.

According to the above-described method, by time-dividing one RU and allocating the time-divided RU to multiple STAs, waste of resource may be reduced.